The Myc proto-oncogene is overexpressed in a high percentage of human cancers. Our lab previously showed that deregulation of protein synthesis is essential for the development of Myc-induced tumors. Overexpression of Myc disrupts normal modes of translational regulation;specifically, a switch in translation initiation mechanisms that normally occurs at a specific stage of the cell cycle is abrogated when Myc is overexpressed. Importantly, several key cell cycle regulators are translated via an alternative mode of translation initiation, Internal Ribosome Entry Site (IRES) mediated translation. The p58 isoform of cyclin dependent kinase 11 (CDK11) is one prominent example. During mitosis CDK11 mRNA is translated exclusively via an IRES element. We observed a decrease in CDK11/p58 protein levels in a Myc-induced lymphoma model, which correlated with a loss of genome integrity. Surprisingly, restoration of normal protein synthesis rescued the expression of CDK11/p58 and prevented tumor development. The experiments proposed here will build upon these preliminary data to establish a molecular mechanism for the deregulation of translation initiation subsequent to Myc hyperactivation. This work will also characterize other mRNAs that display aberrant translation downstream of Myc hyperactivation. Additionally we will gain further insight into the role of deregulated protein synthesis in Myc-induced tumorigenesis. We will address the question of the role of translational regulation in Myc-induced tumorigenesis using both biochemical and genetic approaches as outlined in the specific aims. In Aim 1 we will define the mechanism by which oncogenic Myc activation results in a decrease in CDK11/p58 translation. Specifically we will characterize the proteins that physically associate with the CDK11/p58 IRES and are required for IRES mediated translation. In Aim 2 we will determine the effect of hyperactivation of Myc on the translational control of other cell cycle regulators during mitosis. We will determine those cell cycle regulators whose translation is sensitive to Myc activity using novel biochemical and molecular genetic approaches. The proposed experiments will provide much needed mechanistic insight into the process of Myc-induced tumorigenesis, specifically highlighting the role of deregulated protein synthesis. The results obtained from these experiments will guide the development of future therapeutic intervention directed at tumors harboring hyperactive Myc, which have been refractory to current standard treatments. PUBLIC HEALTH RELEVANCE: The Myc proto-oncogene is activated in a high percentage of human cancers resulting in a disruption of normal translational regulation, which is required for Myc-induced tumorigenesis. The experiments outlined in this proposal will define a molecular mechanism for the deregulation of protein synthesis observed upon Myc- hyperactivation and characterize the translational regulatory networks that are disrupted. The results obtained will identify novel targets for future therapeutic intervention in tumors with hyperactive Myc.